The invention relates to valves for controlling liquid flow, and is particularly adapted for use in fuel valves for aircraft. However, it is understood that the invention may have other applications.
Current military requirements necessitate cargo and other types of aircraft to have aerial refueling capability. Such capability requires that there be fuel level control valves on the aircraft which will open and allow fuel flow during an aerial refuel hookup. In addition, many new generation aircraft require that fuel be redistributed between tanks located in different parts of the aircraft during flight in order to maintain critical center of gravity control of the aircraft. This requires a dependable control valve which will allow fuel to flow from point to point as required.
In the past, valves used to perform these functions have been controlled by solenoids. Such valves are available in two different types: normally closed and normally open. A normally closed type valve requires that the solenoid be energized in order for the valve to open and fuel to flow, whereas a normally open type valve allows fuel to flow with the solenoid deenergized. Solenoid failure has been found to be a fundamental problem with both types of valves. In addition the valves require constant power while the solenoid is energized and if the amount of "solenoid on" time they are subject to is high, the life expectancy of the solenoid can be greatly reduced.
Accordingly, it is an object of the present invention to provide a valve system for the control of liquid flow, and especially for the control of fuel flow in an aircraft during refueling that is more reliable than previous systems.
It is another object of the present invention to provide a normally closed dual solenoid actuated valve system that can function upon the failure of one solenoid.
It is still another object of the present invention to provide a dual solenoid controlled liquid valve system in which each solenoid is used less often than solenoids in previous systems.